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Saturday, March 12, 2016

Windstorm Update: Could This Be a Big Fizzle over Puget Sound?

There are some forecasts where the uncertainties are very large and this is one of them. There has been a lot of press about the Sunday forecast, such as the Seattle Times headline below:

The National Weather Service has a high wind warning up right now. Not a watch. That means they are very sure that very strong winds are imminent.

But I am very worried about this forecast. First, the storm hasn't even formed yet. Here is the latest infrared satellite imagery (8:15 PM)....no circulation or really anything apparent over the eastern Pacific,

And the latest model runs are really pulling back the threat for the Puget Sound interior.

Let me illustrate. The UW WRF forecast for 8 AM Sunday (remember we will be shifting to Daylight Savings Time) is much less threatening: the low is not as deep and is more amorphous.

At 2 PM it is stronger, but the pressure gradients are weaker than earlier runs and the low is in a dumb bell shape, which works against really strong winds. Windy on the southern WA coast at this time (gusts to 40-50 mph perhaps).

The low lifts over southern Vancouver Island at 5 PM, with the pressure gradients over Puget Sound not that strong. Yes, it will get blustery during the latter afternoon, but we are talking about 30-40 mph gusts, NOT the 60-70 mph gusts being advertised. Thus, we are talking about a relatively tame event.

So we start with a system in which the solutions are not stable...not good.

Now lets take a looks at the NWS Short Range Ensemble Forecasting (SREF) System, which uses many model runs (see below). Oh-oh. The models are ALL OVER THE PLACE, with some providing very little wind tomorrow afternoon/evening (00-14th is tomorrow at 5 PM). The strong wind simulations are outliers and the mean of the ensembles is only 15 knots (sustained wind).

The other major NOAA/NWS ensemble is the GEFS ensemble, and it shows a mean sustained wind at 14 knots, with lots of spread of the solutions

Bottom line: really strong winds over Puget Sound is no sure thing. I suspect that tomorrow will be a tamer version of this week's wind event and nothing exceptional. But there is considerable uncertainty and there is perhaps at 10-25% chance this will be a notable event. About the same probability of Marco Rubio winning the Florida primary.

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19 comments:

The NWS whiffed badly on the Wed/Thur Puget Sound wind event. They didn't issue a wind advisory until 4am thursday, at which time everybody's trees were swaying wildy and their garbage cans were flying down the street. I suspect they are being overly cautious this time.

FORECAST CONFIDENCE TAKING A HIT THIS EVNG REGARDINGTHE DETAILS AND STRENGTH OF THE ADVERTISED WINDSTORM FOR SUNDAYPM. THIS AFTER A FEW DAYS OF UNCERTAINTY AND THE EVENTUALDEVELOPMENT OF MODEL CONSENSUS OF A STRONG WINDSTORM OVER THEPAST 24 HOURS. ALL MODELS...AND NOW SATELLITE IMAGERY...SHOW THEQUICK DEVELOPMENT OF A LOW CENTER AROUND 42N 135W. ALL MODELS THENTAKE THE LOW NE TOWARD THE WA COAST ON SUNDAY AFTN. THIS HAS NOTCHANGED.

HOWEVER...THE 00Z GFS SHOWS A MORE ELONGATED LOW CENTER NOW THATSTILL CROSSES TATOOSH ISLAND BUT THEN TAKES IT OFF MORE TO THENNE. THE MORE NORTHWARD TRACK BEYOND TOMORROW AFTN AND ELONGATEDSTORM STRUCTURE ARE LESS IDEAL. IT NOW PEAKS THE OLM-BLI GRADIENTNEAR 5.5 MB ARND 00Z...WHICH IS STILL QUITE RESPECTABLE BUTNOTHING WE HAVE NOT SEEN ALREADY THIS WINDY MARCH. THE UW WRF-GFSREFLECTS THIS TREND AS WELL.

THE 00Z NAM IS A BIT MORE BULLISH...PEAKING INTENSITY OF THE LOWAT 981 MB AS IT IS CROSSES THE OLYMPIC PENINSULA. THE OLM-BLIGRADIENT THEN PEAKS NEAR 9-10 MB...WITH 925-850 MB LAYER WINDSREACHING 50 KT ARND 03Z. WITH A MIXING HEIGHT OF ABOUT 3000-4000FEET AT THE TAIL END OF DAYTIME HEATING...THIS COULD EASILY MIXDOWN GUSTS NEAR 50-55 MPH...AGAIN RESPECTABLE AND IMPACTFUL BUTNOT AS STRONG AS CURRENTLY FORECAST.

THE 00Z HI-RES ARW STILL SHOWS A MORE COMPACT AND ROBUST LOW ANDMAY BE THE MOST BULLISH IN SHOWING WIND POTENTIAL.

CONSIDERING THE ALREADY-ISSUED SUITE OF WARNINGS...ANDCONSIDERING THAT THIS WILL STILL LIKELY BE A STRONG ENOUGH STORMTO CAUSE SOME POWER OUTAGES AND TREE IMPACTS...SEEMS WISE TOSIMPLY LEAVE THE FORECAST ALONE AND WAIT LATER GUIDANCE. EVEN IFTHE SUNDAY WINDSTORM IS MERELY SIMILAR IN STRENGTH TO OTHERWINDSTORMS OF THE PAST WEEK...IT WILL STILL KEEP UTILITIES BUSYRESPONDING TO OUTAGES AND BRING DOWN A FEW MORE TREES.

FOLLOWING THE EXIT OF THE LOW...WRN WA WILL STILL HAVE A MOIST ANDUNSTABLE AIR MASS THROUGH TUE...WITH LOW-LEVEL ONSHORE FLOW. SOEXPECT TO SEE SHOWER ACTIVITY CONTINUING...WITH ACTIVITY MOSTFOCUSED OVER THE MTNS AND IN A PUGET SOUND CONVERGENCE ZONE.HANER

It's happened before. I have huge trees and when the winds are 60+, I leave! One time I left and there wasn't even a puff, maybe 5mph. That and I can't sleep during big winds not hitting 60+.I'm all for a 'fizzle'!

Mark's quote of the forecast discussion above was a helpful reminder -- sometimes in the excitement I forget to check, and invariably they provide useful insight into level of forecasting uncertainty. "Bottom Line" from 3AM iteration (case changed):

NATIONAL WEATHER SERVICE SEATTLE WA301 AM PDT SUN MAR 13 2016"...Bottom line is that confidence in a significant windstorm is notas high as it was 12 or 24 hours ago. The high wind warnings wereissued Saturday afternoon...and they will remain in effect. Weare lowering the wind speeds somewhat -- essentially forecastinghighest winds of 40 to 45 mph with gusts 55 to 60 mph rather thanthe 40 to 50 mph with gusts 70 mph of the previous forecast. Inmost areas the strongest winds should occur this afternoon andevening..."

Last HRRR I saw still showed respectable sustained winds and gusts. I walk around wetlands as often as I can and local water tables seem quite high -- shallow rooted trees aren't likely to take much urging before they fall over. Caution still seems appropriate.

From the above FX, perhaps the most important element of the communication:

"FORECAST CONFIDENCE TAKING A HIT THIS EVNG ......"

Cliff, have you ever considered trying to illustrate the importance of uncertainty (the unknown) in forecasting? There is an enormous amount of well substantiated work done on how humans tend to "diagnose" rather than manage probabilities, in terms of decision making. You are no doubt aware of this work by Danniel Kahnemann, Gerd Gergerenzer and so many others who study risk. When the above weather experts honestly and unambiguously communicate uncertainty, they are communicating the key to how to proceed, in terms of risk. The problem is in the end user. If we are not skilled in decision making under terms of uncertainty, we under value that gift that they are giving us - a clear statement of the magnitude of the unknown. The average end user is much more familiar with simple or complex problems where solution is much more linear and conclusive.

I think you are right in consistently pointing out exageration in newspaper headlines and other pop media info flows. However, the real problem is that they shout out certainty simply because their audience demands it. The essence of decision making study shows quite well that humans have been trained and conditioned both culturally and genetically to misshandle risk. You must be well aware of this popular miss perception, the "60% chance of showers" problem being a classic example.

It may be a hopeless goal, but it has been shown that decision making can improve if people can better understand the pervasiveness of uncertainty, and that accepting the reality of uncertainty is not "crippling" in terms of decision making, rather it then frames the problem as a risk management problem, not purely a diagnosis problem.

The significant disconect between the climate scientists, ecologists, etc and us 99% is primarilly a disconnect of perception - and consequent failure of communication - of risk. That is abundantly demonstrated by the popular perception of the reliability of models. Our common sense tells us "if the models are off, they are deceptive". The expert knows otherwise. They know how to factor uncertainty. We do not. We expect a certain diagnosis and any indication that that is lacking immediately prompts a judgement that uncertainty = failure.

Your blog could really contribute to a better understanding of risk framing I think. You have trust, a big audience and a varied audience but for the most part, the audience is very limited in expertise of either weather or climate, both domains where uncertainty is highly relevant in evolving toward "best known".

Thank you for being a voice of reason in a sea of sensationaism. I'm tired of power outages, exoectancy of trees coming down on our or neighbors properties. I'm just fine with your forecast discussion. This would be at least the 4th huge wind event in our area (Stanwood/Camano), in just the last few months.

Low is deeper than forecast and the NAM is handling the structure and depth of the low BETTER than the GFS in the short term.

Recent HRRR has the low at 977nm on the tip of the Olympic Peninsula. That's almost 10mb lower than the GFS was saying at times yesterday and still 5-6mb lower than the GFS on the run coming out late this morning.

Actual obs have the low already at 980, while the GFS showing 989 last night and 985 this morning.

Still the track is perfect for a huge blow to the Puget sound, but its no fizzle either.

You got that fork and plate of 'crow' at the ready, Cliff? :) From what I'm seeing on the latest sat imagery, the low looks like it may be tracking closer to the NAM/ECMWF path (unless it makes a hard-left in the next hour)... Ruh-roh!

Those who are reading this post might want to look at the next update: http://cliffmass.blogspot.com/2016/03/a-beautiful-storm.html

More to consider than just "mb" of the low ... there are also gradient, terrain, location and track (plus more I'm sure I missed). This track seems like it might veer a small bit to the NW a bit because of the parent low further out in the Pacific (maybe).

But it will still cross at South Vancouver / Forks ... small (moderate) gradient though. Windy it will be. :)

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